Today's credential formats do not offer the flexibility to meet the needs of high-scale/high-availability web services. For example, X.509 is very good for asymmetric key authentication, but is very difficult to use for anything else. One reason for this is that X.509 is based on Asynchronous Syntax Notation One (ASN.1) and requires compiling of specialized code to process an X.509 license. X.509 allows extensions, but the extensions are limited and not widely supported. Kerberos is another common format which focuses on arbitrated authentication using symmetric keys, but is not designed to be used for other types of authentication. Kerberos has an extensibility field, but there are no conventions or interoperability. EXtensible resource Markup Language (XrML), version 1, is limited because it doesn't support delegation and many other concepts and focuses on digital rights management.
Thus, there is a need for a format that can be used for different authentication and authorization purposes and that provides the flexibility to meet the demands of high-scale/high availability web services.